Adding grains for ALT Linux

Addresses issue #3444. Tagging @valintinr.

This OS uses /etc/altlinux-release (and /etc/fedora-release, /etc/redhat-release and /etc/system-release) for identification. With a release file that looks like:

ALT Linux Sisyphus (unstable)

...you get grains that look like:

 'lsb_distrib_codename': 'unstable',
 'lsb_distrib_id': 'altlinux',
 'lsb_distrib_release': 'Sisyphus',
 'os_family': 'RedHat',
 'oscodename': 'unstable',
 'osfullname': 'altlinux',
 'osrelease': 'Sisyphus',

This seems to be consistent with the CentOS 6.3 and Arch Linux boxes that I compared against.